Polar bears depend on sea ice

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					FACT SHEET 2:
Polar bears depend on
sea ice
Projections of sea ice decline in the future spell trouble.
Forecasts of summer sea ice from a range of climate
models suggest reductions of 50 % or more by 2050,
with some models projecting the complete
disappearance of summer sea ice in a similar time frame.
Such reductions in sea ice will drastically shrink marine
habitat for polar bears, walrus, ice-inhabiting seals, and
some seabirds, pushing some species toward extinction.        Ice-living seals
It is difficult to imagine the survival of ringed seals and   Ice-living seals, including the ringed seal, ribbon seal,
polar bears in the absence of summer sea ice.                 and bearded seal, are particularly vulnerable to
                                                              projected reductions in Arctic sea ice because they give
The polar bear                                                birth to and nurse their pups on the ice and use it as a
Polar bears are intimately tied to the sea ice, where they    resting platform. They also do much of their foraging
hunt ringed seals and other ice-associated seals, and use     on the ice. Ringed seals are likely to be the most highly
ice corridors to move from one area to another.               affected species of seal because all aspects of their lives
Pregnant females build their winter dens in areas with        are tied to sea ice. They require sufficient snow cover
thick snow cover on land or on sea ice. When females          to construct lairs and the sea ice must be stable enough
emerge from their dens with their cubs, the mothers           in the spring to successfully rear young. Earlier ice
have not eaten for 5 to 7 months. Their seal hunting          break-up could result in premature separation of
success, which depends on good spring ice conditions,         mothers and pups, leading to higher death rates among
is essential for the family's survival. Changes in ice        newborns.
extent and stability are thus of critical importance. The
earliest impacts of warming would be expected to occur
at the southern limits of the polar bears' distribution,
such as James and Hudson Bays; such impacts have
already been documented in recent years.

Later formation and earlier break-up of sea ice means a
longer period of fasting annually for female polar bears,
and their reproductive success is tightly linked to their
fat stores.
Females in poor condition have smaller litters and
smaller cubs that are less likely to survive.
Climate change could also increase bear deaths directly.
For example, increased frequency or intensity of spring
rains could cause dens to collapse, resulting in the
death of females and cubs. Earlier spring break up of
ice could separate traditional den sites from spring
feeding areas, and young cubs forced to swim long
distances from breeding areas to feeding areas would
not be likely to survive.

The only foreseeable option that polar bears would
have is to adapt to a land-based summer life-style, but
competition, risk of hybridization with brown and
grizzly bears, and increased human interactions would
then present additional threats to their survival as a
                                                              These two images, constructed from satellite data, compare arctic
species. The loss of a pinnacle species such as the polar     sea ice concentrations in September of 1979 and 2003.
bear is likely to have significant and rapid consequences     September is the month in which sea ice is at its yearly minimum and
for the ecosystems they currently occupy.                     1979 marks the first year that data of this kind became available in
                                                              meaningful form. The lowest concentration of sea ice on record was
                                                              in September of 2002 and 2003 was very close to that record low.
Cascading impacts on species                                  These changes will have significant implications for the
Climate-related changes are likely to cause cascading         ability of caribou and reindeer populations to find food
impacts involving many species of plants and animals.         and raise calves. Future climate change could thus
Compared to ecosystems in warmer regions, Arctic              mean a potential decline in caribou and reindeer
systems generally have fewer species filling similar roles.   populations, threatening human nutrition for
Thus when Arctic species are displaced, there can be          indigenous households and a whole way of life for
important implications for species that depend upon           Arctic communities.
them. For example, mosses and lichens are particularly
vulnerable to warming. Because these plants are               Aquatic mammals and waterfowl
important winter food sources for reindeer/caribou            The distribution of aquatic mammals and waterfowl
and other species and are the base of important food          will likely extend northward as habitats change with
chains, their decline will have far-reaching impacts          warming. Seasonal migration is also likely to occur
throughout the ecosystem. If reindeer and caribou             earlier in spring and later in fall if temperatures are
populations decline, that will impact species that hunt       warm enough. Breeding ground suitability and access to
them, including wolves, wolverines, and human beings,         food will be the primary drivers of changes in
as well as species that scavenge on them, such as Arctic      migration patterns. For example, wetlands are
foxes and various birds. Because some local                   important breeding and feeding grounds, and as
communities       are    particularly   dependent      on     permafrost thaws, more wetlands are likely to appear,
reindeer/caribou, their well-being will also be impacted.     promoting the earlier northward migration of southerly
                                                              wetland species or increasing the abundance and
Ice crust                                                     diversity of current high latitude species. However, a
Ice crust formation resulting from freeze-thaw events         parallel earlier timing of the availability of local food
affects most Arctic land animals by encapsulating their       must also occur for these outcomes to be realized.
food plants in ice, severely limiting forage availability
and sometimes killing the plants. Lemmings, musk              Mammal and bird species moving northward are likely
oxen, and reindeer/caribou are all affected, and              to carry new diseases and parasites that pose new
dramatic population crashes resulting from ice crusting       threats to arctic species. Another potential downside of
due to freeze-thaw events have been reported and their        the northward migration of southerly species is that
frequency appears to have increased in recent decades.        they may out-compete northern species for habitat and
The projected winter temperature increase of 6°C by           resources. Northerly species may have diminished
late this century (average of the five ACIA model             reproductive success as suitable habitat either shifts
scenarios) could result in an increase of alternating         northward or perhaps declines in availability or access.
periods of melting and freezing.

Inuit of Nunavut in Canada report that caribou
numbers decrease in years when there are many freeze-
thaw cycles. Swedish Saami note that over the last
decade, autumn snow lies on unfrozen ground rather
than on frozen ground in summer grazing areas and
this results in rotten and poor quality spring vegetation.

Caribou and reindeer
Caribou and reindeer are of primary importance to
inland peoples throughout the Arctic for food, shelter,
fuel, tools, and other cultural items. Caribou and
reindeer herds depend on the availability of abundant
tundra vegetation and good foraging conditions,
especially during the calving season. Climate-induced
changes to Arctic tundra are projected to cause
vegetation zones to shift significantly northward,
reducing the area of tundra and the traditional forage
for these herds. Freeze-thaw cycles and freezing rain
are also projected to increase.

				
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posted:5/14/2011
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